EP0169126 (CLEXTRAL) describes a process for preparing a composite foodstuff using an extruder having several successive zones, in which extruder a stream of food substance leaving a first zone comprising a twin-screw unit is split into several independent streams in a second zone comprising two single-screw units, the two independent streams undergoing distinct processing operations, especially distinct colorations, in this second zone and being recombined in a third zone comprising a die to form a single composite product, especially a product containing two differently colored and/or flavored co-extruded parts.